Membrane pressure sensor comprising silicon carbide and method for making same

ABSTRACT

The invention concerns a pressure sensor ( 1 ), able to operate at high temperature and measure the pressure of a hostile medium, comprising: 
     a sensing element ( 4 ) integrating a membrane ( 8 ) in monocrystalline silicon carbide, made by micro-machining a substrate in polycrystalline silicon carbide, a first surface of membrane ( 8 ) intended to contact said medium, a second surface of membrane ( 8 ) comprising membrane deformation detection means ( 9 ) connected to electric contacts ( 10 ) to connect electric connection means ( 11 ), the surfaces of sensing element ( 4 ) contacting said medium being chemically inert to this medium; 
     a carrier ( 5 ) to support sensing element ( 4 ) so that said first surface of membrane ( 8 ) may be contacted with said medium and the second surface of membrane ( 8 ) may be shielded from said medium, carrier ( 5 ) being in polycrystalline silicon carbide; 
     a seal strip ( 6 ), in material containing silicon carbide, brazed between carrier ( 5 ) and sensing element ( 4 ) to protect the second surface of membrane ( 8 ) from any contact with said medium.

TECHNICAL FIELD

The present invention relates to a membrane pressure sensor containingsilicon carbide. It also concerns the manufacture of the sensing elementof the sensor.

PRIOR ART

With micro-electronic techniques it is possible to produce miniaturepressure sensors using collective manufacturing processes. Small-sizedsensors can therefore be produced at low cost. They provide thepossibility of producing a sensor and its associated electronics on onesame carrier.

Micro-machined pressure sensors are known, made up of a silicon membranea few tenths of a μm in thickness. The difference in pressure betweenthe two surfaces of the membrane may be detected by measuring the recessstresses by means of piezoresistive gauges obtained by ion diffusion orimplantation. These piezoelectric gauges have high sensitivity andextensive mechanical stability due to the monocrystalline structure ofthe silicon used. Between each gauge and the substrate on which they arefabricated, electric insulation is achieved using reverse junctions.This has the disadvantage of limiting the range of operating temperatureof these sensors to a maximum of 125° C. due to the strong leakagecurrent at the reverse junction, and of causing a high noise level(thermal noise and piezoelectric junction noise) which reduces thedynamic range. A further disadvantage of piezoresistive gauges for theirusual use results from the direct exposure of these gauges and frommetallisation related to the fluid whose pressure is to be measured,which submits these elements to the effects of humidity and corrosiveagents.

Pressure sensors are also known with piezoresistive gauges embedded inthe silicon. However, these sensors cannot be used for temperatures over200° C.

Pressure sensors made on SOI (Silicon-On-Insulator) substrates are alsoknown. These sensors do not have the disadvantages due to leakagecurrent or to noise on account of the intermediate insulating layer.They may be used up to temperatures in the order of 400° C.

Research is currently focusing on techniques using silicon carbide,which are able to provide products able to operate up to temperatures inthe order of 700°C.

These micro-machined pressure sensors are encapsulated in relation totheir intended use. Pressure sensors for the automotive industry andthose intended to be mounted on a board are generally encapsulated inpre-moulded “dual-in-line” type casings. Some casings may be custom-madein relation to the intended application, by designing a pre-mouldedhousing in thermoplastic material to ensure the best possible mechanicalintegration of the sensor, and by using the “dual chip” technique forthe incorporation of associated electronics. In practice, this type ofencapsulation offers very few application possibilities and the presenceof thermoplastic material imposes a maximum temperature.

The use of pressure sensors in a hostile environment requires givingconsideration to the restraints of temperature, and the type of fluidwhose pressure it is sought to measure, in particular its corrosivenature. So as to protect the membrane of the sensor from its immediateenvironment, encapsulation frequently integrates means for the hydraulictransmission of the pressure to be measured, combining for examplesilicon oil and a membrane or a metal bellow device. This solution hasthe disadvantage of increasing the cost of the sensor. Also, silicon oildoes not withstand a temperature greater than 300° C. For highertemperatures, mercury may be used, but regard must be given to itsharmful effect on the environment.

In a hostile medium, encapsulation may further use materials such asstainless steel and ceramic in order to protect the silicon part of thesensor. The sensor membrane may be protected from the medium, whosepressure is to be measured, by another membrane which directly coversthe first membrane (enabling operation of the sensor up to 300° C.) orby a mechanical pressure transmission system using a diaphragm (whichenables operation of the sensor up to 450° C).

U.S. Pat. No.4,898,035 discloses a ceramic pressure sensor, for themeasurement in particular of the pressure in the cylinder of an internalcombustion engine. This sensor comprises a sensing element integrating amembrane, a first surface of the membrane being intended to contact themedium whose pressure is to be measured. The second surface of themembrane supports membrane deformation detection means connected toelectric conductors, not shown. The membrane being is ceramic, itssurface intended to contact the hostile medium is chemically inertrelative to this medium. The carrier of the sensing element supportsthis element so that one of the surfaces of the membrane is in contactwith the hostile medium and the opposite surface is shielded from thiscontact. The carrier and ring disk are metallic. The seal between theinside of the sensing element and its carrier is ensured by theconnection layer in glass or a brazing material.

U.S. Pat. No. 4,894,635 discloses a stress sensor, for example apressure sensor. This sensor is intended to operate at high temperature.It is also intended for use in a hostile medium such as vehicle engines.The sensing element is formed from a substrate in ceramic. It comprisesa membrane of which one surface is exposed to the medium whose pressureis to be measured, and the other surface supports the detection means.Parts act as support for the sensing element. They place one of themembrane surfaces in contact with said medium and prevent the surfaceopposite the membrane from coming into contact with this medium. Theseal is ensured by a toroidal joint.

Document DE-A-196 01 791 discloses a membrane detector and its method ofmanufacture. The detector is a micro-machined structure comprising adeformable membrane integral with a peripheral part enabling itsdeformation. The membrane comprises a layer in SiC and a layer in SiO2.The detection elements are placed on the electric insulating layer.

U.S. Pat. No. 4,706,100 discloses a piezoresistive pressure sensorcomprising: a substrate of monocrystalline silicon, an epitaxied layerof monocrystalline □-SiC, piezoelectric resistances formed by diffusionor implantation in the epitaxied layer, electric contacts to connect thepiezoelectric resistances and a cavity formed on the rear surface of thesubstrate to form a membrane.

DESCRIPTION OF THE INVENTION

The present invention was designed to remedy the disadvantages ofpressure sensors of the prior art. It can be used to produce a miniaturepressure sensor manufactured by collective manufacturing processes,compatible with resistance to a severe environment (high temperature,chemically aggressive measuring medium), compatible with simplifiedencapsulation and having a low production cost.

The subject of the invention is therefore a pressure sensor able tooperate at high temperature and to measure the pressure of a hostilemedium, comprising:

a sensing element integrating a membrane in monocrystalline siliconcarbide and produced by micro-machining a substrate in polycrystallinesilicon carbide, a first surface of the membrane being intended to beplaced in contact with said medium, a second surface of the membranecomprising means to detect membrane deformation connected to electriccontacts for connection of the electric connection means, the surfacesof the sensing element intended to be in contact with said medium beingchemically inert relative to this medium;

a carrier supporting the sensing element so that said first surface ofthe membrane may be contacted with said medium and the second surface ofthe membrane may be shielded from contact with said medium, the carrierbeing in polycrystalline silicon carbide;

a seal strip in material containing silicon carbide brazed between thecarrier and the sensing element to protect the second surface of themembrane against any contact with said medium.

If the sensor is intended to measure absolute pressure, the carrier maycomprise a sealed closing part so that a vacuum can be set up inside thecarrier.

Advantageously, the carrier is tube-shaped, the sensing element closingone of the tube ends, the first surface of the membrane being directedtowards the outside of the tube. It may then be provided with a threadwith which it can be screwed onto a reservoir containing the medium.

An insulating interface layer may be provided between the membrane andthe substrate part of the sensing element. This insulating interfacelayer may be in a material chosen from among silicon oxide, siliconnitride and carbon-containing silicon.

The electric contacts equipping the detection means may be in a silicidecontaining tungsten. The connection between the electric contacts andthe electric connection means may be obtained by a solder materialwithstanding high temperatures. This solder material may be a silicidecontaining tungsten. Conductor means may also be provided forming aspring to ensure the connection between the electric contacts and theelectric connection means.

The detection means may comprise at least two piezoresistive gauges, inmonocrystalline silicon carbide for example.

A further subject of the invention is a method of manufacture bymicro-machining at least one membrane sensing element for a pressuresensor able to operate at high temperature and to measure the pressureof a hostile medium, comprising the following steps:

a) producing a layer of monocrystalline silicon carbide on one surfaceof a substrate containing polycrystalline silicon carbide,

b) fabricating, on the free surface of the monocrystalline siliconecarbide layer, means to detect membrane deformation,

c) fabricating electric contacts on said free surface to connect thedetection means to the electric connection means,

d) forming the membrane of said sensing element by removing materialfrom the other surface of the substrate, so as only to preservepolycrystalline silicon carbide.

The fabrication of said layer of monocrystalline silicon carbide maycomprise:

transferring a first layer of monocrystalline silicon carbide onto saidsurface of the substrate,

depositing by epitaxy a second layer of monocrystalline silicone carbideon the first layer in order to obtain said monocrystalline siliconcarbide layer of controlled thickness.

The production of said layer of monocrystalline silicon carbide mayentail the use of a wafer in monocrystalline silicon carbide in which alayer has been defined by a layer of microcavities generated by

depositing by epitaxy a second layer of monocrystalline silicone carbideon the first layer in order to obtain said monocrystalline siliconcarbide layer of controlled thickness.

The production of said layer of monocrystalline silicon carbide mayentail the use of a wafer in monocrystalline silicon carbide in which alayer has been defined by a layer of microcavities generated by ionimplantation, said wafer being bonded to said surface of the substrateand then cleaved at the layer of microcavities so as only to preservesaid layer defined on the substrate. Preferably, cleavage of the waferis obtained by coalescence of the microcavities resulting from heattreatment. Also preferably, the bonding of said wafer onto the substrateis obtained by molecular bonding.

Before the step to produce said layer of monocrystalline siliconcarbide, an insulating interface layer may be deposited on the surfaceof the substrate on which said layer is to be made.

During the membrane formation step, the removal of matter from the othersurface of the substrate may be conducted using an operation chosen fromamong mechanical machining and chemical etching.

According to one variant of embodiment, the method may comprise thefollowing preliminary steps:

machining a substrate to obtain a bump of complementary shape to theshape of the desired sensing element as seen from the hostile mediumside,

depositing a layer of polycrystalline silicon carbide on the substrateon the bumping side,

levelling the previously deposited layer down as far as the tip of thebump, steps a) and d) then being conducted in the following manner:

a) the layer of monocrystalline silicon carbide is formed on thesubstrate on the levelled layer side,

d) the membrane of said sensing element is formed by removal of theinitial substrate.

The layer of chemically inert material deposited on the substrate on thebumping side must be sufficiently thick to ensure good mechanicalresistance when the initial substrate is removed.

The substrate may be in silicon.

The fabrication of said layer of monocrystalline silicon carbide maycomprise:

transferring a first layer of monocrystalline silicon carbide onto thesubstrate,

depositing by epitaxy a second layer of monocrystalline silicon carbideon the first layer of monocrystalline silicon carbide in order to obtainsaid monocrystalline silicon carbide layer of controlled thickness.

Advantageously, the depositing step of a layer of polycrystallinesilicon carbide may be made by CVD for example. The levelling step maybe conducted by mechanical-chemical polishing.

According to this variant of the method, the production of said layer ofmonocrystalline silicon carbide comprises the use of a wafer inmonocrystalline silicon carbide in which a layer has been defined by alayer of microcavities generated by ion implantation, said wafer beingbonded to the substrate on the side of the levelled layer then cleavedat the layer of microcavities so as only to preserve said layer definedon the substrate. Preferably, cleavage of the wafer is obtained bycoalescence of the microcavities resulting from a heat treatment. Alsopreferably, the bonding of said wafer to the substrate is obtained bymolecular bonding.

Before the step to produce said layer of monocrystalline siliconcarbide, an insulating interface layer may be deposited on the surfaceof the substrate on which said first layer is to be formed.

During the membrane formation step, the removal of the initial substratemay be obtained by chemical etching.

According to another variant of embodiment, the method may comprise thefollowing preliminary steps:

machining a substrate to obtain a bump of complementary shape to theshape of the desired sensing element as seen from the hostile mediumside,

depositing a layer of polycrystalline silicon carbide on the substrateon the bumping side,

levelling the previously deposited layer so that above the bumping onlythe desired membrane thickness subsists, steps a) and d) then beingconducted in the following manner:

a) the layer of monocrystalline silicon carbide is formed on saidlevelled layer,

d) the membrane of said sensing element is formed by removal of theinitial substrate.

The substrate may be in silicon.

Advantageously, the depositing step of a layer of polycrystallinesilicon carbide may be made by CVD for example. The levelling step maybe conducted by mechanical-chemical polishing.

According to this other variant of embodiment, the fabrication of thelayer of monocrystalline silicon carbide may be obtained using a waferin monocrystalline silicon carbide in which said layer has been definedby a layer of microcavities generated by ion implantation, said waferbeing bonded to the substrate on the side of the levelled layer thencleaved at the layer of microcavities so as only to preserve the layerof monocrystalline silicon carbide on the substrate. Preferably,cleavage of the wafer is obtained by coalescence of the microcavitiesresulting from a heat treatment. Also preferably, the bonding of saidwafer to the substrate is obtained by molecular bonding.

During the membrane formation step, the removal of the initial substrateof silicon may be obtained by chemical etching.

An insulating interface layer may be deposited on the levelled layerbefore placing said layer of monocrystalline silicon carbide. During theforming of the detection means, the remaining part of themonocrystalline silicon carbide layer may be removed.

If the method of the invention is a collective method for fabricatingsensing elements from one same substrate, a final substrate cutting stepmay be provided to obtain separate sensing elements.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages anddistinctive characteristics will become better apparent on reading thefollowing description given as an illustrative example and thereforenon-restrictive, accompanied by the appended drawings in which:

FIG. 1 is an axial section view of a membrane pressure sensor, ofrelative pressure type, according to the present invention,

FIG. 2 is an axial section view of a membrane pressure sensor, ofabsolute pressure type, according to the present invention,

FIGS. 3A to 3D illustrate a first embodiment method for the sensingelements of pressure sensors according to the present invention,

FIGS. 4A to 4E illustrate a second embodiment method for the sensingelements of pressure sensors according to the present invention,

FIGS. 5A to 5C illustrate a third embodiment method for the sensingelements of pressure sensors according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a pressure sensor 1, according to the invention, mounted onan orifice opening into wall 2 of a reservoir (it may be an enginecylinder). The inside 3 of the reservoir contains a hostile medium whosepressure is to be measured. The pressure sensor 1 comprises a sensingelement 4 fixed to one end of a carrier 5 by means of a seal strip 6.

The carrier 5, in this example of embodiment, is tubular shaped. Withthis shape it can be easily fixed, by screwing, into an appropriatehousing in wall 2 of the reservoir. The sensing element 4 is fixedperipherally to the end of carrier 5 located on the positioned towardsthe inside of the reservoir 2 is therefore subjected to the innerpressure of the reservoir, and the opposite surface of the sensingelement is subjected to outside pressure.

The sensing element 4 comprises a thicker peripheral part 7 and athinner central part or membrane 8. The sensing element, depending uponthe range of pressure to be measured, is designed so that the peripheralpart 7 does not undergo any or scarcely any deformation, while thecentral part or membrane 8 will undergo deformation. Membranedeformation is detected by detection means 9, by piezoresistive gaugesfor example positioned on the surface of membrane 8 that is not exposedto the hostile medium. The sensing element 4 also comprises, on itssurface not exposed to the hostile medium, electric contacts 10 ensuringthe connection between the piezoresistive gauges and an electroniccircuit processing the signals given by the gauges.

This electric connection must be made taking into account the hightemperature to which the pressure sensor may be submitted. As shown inFIG. 1, it is possible to use a metal wire exerting a pressure on theelectric contact. Therefore wires 11, maintained by ceramic screws 12 oncarrier 5, enable electrical connection with contacts 10 through aspring effect. It is also possible to solder the electric wires to thecontacts using a solder material which withstands high temperatures, forexample by using a material made up of a silicide containing tungsten.

Carrier 5 can be made from a tube of silicon carbide. The sensingelement may be produced using one of the methods described in theremainder of the description. At least the piezoresistive gauges aremade in monocrystalline silicon carbide.

The seal strip 6 brazed for example between the peripheral part 7 of thesensing element and carrier 5 may be made using one of the methodsdisclosed in documents FR-A6 749 787 (Assembly method using a thickjoint of parts in SiC-containing materials by refractory brazing andthick refractory joint so obtained) or FR-A-2 748 471 (Assembly bybrazing of ceramic materials containing silicon carbide). With thesemethods it is possible to directly braze silicon carbide parts to eachother. It is then possible to produce a high temperature pressure sensorwithout using a casing in stainless steel/ceramic and to place themembrane of the sensing element in direct contact with the medium whosepressure is to be measured. This solution enables more precise sensorsto be produced and at lower cost, since it does not involve a transferoperation on account of the casing.

The pressure sensor 13 in FIG. 2 comprises parts which are identical toparts of the sensor in FIG. 1. These parts carry the same referencenumbers.

A closing part 14, in ceramic for example, is sealed to the end ofcarrier 15 opposite the sensing element 4. It is used to set up a vacuuminside the carrier. It comprises two sealed passages 16 used to insert,inside support 15, electric wires 17 intended to be connected tocontacts 10. In this example, the connection of the electric wires 17 tocontacts 10 is made by high temperature solders 18.

The sensing element may be produced collectively from an initialsubstrate. After completing the different steps of the embodimentmethod, the final substrate is cut to obtain sensing elements in theform of chips which are then mounted on their carriers.

FIGS. 3A to 3D are section views illustrating a first embodiment methodfor the sensing elements. For reasons of simplicity, the fabrication ofonly one sensing element is shown.

This first method uses as initial substrate 20 (see FIG. 3A) a so-calledpassive substrate, that is to say which is chemically inert relative tothe medium whose pressure is to be measured. Substrate 20 is inpolycrystalline silicon carbide. An insulating interface layer 21, forexample in silicon oxide, was added for example by deposition on surface22 of substrate 20. A first layer 23 of monocrystalline silicon carbideis transferred to the insulating interface layer 21. This transfer mayadvantageously be made using the transfer method disclosed inapplication FR-A-2 681 472. According to this transfer method, a waferin monocrystalline silicon carbide is bombarded with ions (hydrogen ionsfor example) such as to create a layer of microcavities inside the waferparallel to one its main surfaces. The layer of microcavities issituated at a depth corresponding to the thickness of the layer it iswished to transfer. The wafer is then bonded to substrate 20 such thatthe layer to be transferred is in contact with the interface layer 21.Bonding may be made using the molecular bonding method. Using a suitableheat treatment, the microcavities are caused to coalesce and the waferis cleaved along the layer of microcavities. A layer 23 is obtainedadhering to substrate 20, separated from the remainder of the wafer.

If the doping and thickness of the layer so obtained are insufficient toobtain good reading of the pressure range by the piezoresistive gauges,depositing may be made by epitaxy of a second layer 24 ofmonocrystalline silicon carbide so that it is possible to control thedesired thickness and doping of the membrane. The two layers ofmonocrystalline silicon carbide in this case are denoted by the singlereference 25.

As shown in FIG. 3B, piezoresistive gauges 26 are then formed at pointsof layer 25 determined in relation to the shape of the future membrane.These pieozresistive gauges are produced using a method known to personsskilled in the art, for example by ion implantation and annealing.

On layer 25 a conductor layer is subsequently deposited (for example asilicide containing tungsten) which is then etched to form electriccontacts 27 with the piezoresistive gauges 26 (see FIG. 3C).

Substrate 20 is then machined locally from its rear surface,perpendicular to the gauges, until the monocrystalline silicon carbidelayer 25 is reached in order to form, for each sensing element, amembrane 28 attached to a peripheral part 29. Cross cutting of the finalsubstrate will separate the sensing elements (see FIG. 3D).

FIGS. 4A to 4E are section views which illustrate a second method ofembodiment of the sensing elements. For the same reasons as previously,only the fabrication of a single element is shown.

FIG. 4A shows a substrate 30, in silicon for example, which has beenmachined by chemical etching for example, so as to provide bumps 31 ofblunt cone shape on its upper surface. Each bump corresponds to theformation of a sensing element. Etching using a base may be used (KOHfor example) so that it is possible, from a silicon substrate oforientation 100, to machine cavities with edges oriented along planes111 at 54 °.

Then, on the upper surface of substrate 30, a layer 32 ofpolycrystalline silicone carbide is deposited which follows the contourof the bumped surface of substrate 30 (see FIG. 4B). Layer 32 may bedeposited using a CVD technique (Chemical Vapour Deposition).

The substrate so coated is then levelled, for example bymechanical-chemical polishing to obtain the structure shown in FIG. 4C.Each bump tip is uncovered and each bump 31 is surrounded bypolycrystalline silicon carbide 32.

As for the first described method, a first layer 33 of monocrystallinesilicon carbide is transferred to the levelled substrate. A second layer34 of monocrystalline silicon carbide may optionally be epitaxied ontothe first layer 33. Layers 33 and 34 form layer 35 of monocrystallinesilicon carbide (see FIG. 4D). The epitaxied layer 34 is used to controlthe thickness of the membrane.

Then, in the same manner as for the first described method, thepiezoresistive gauges 36 and their electric contacts 37 are formed (seeFIG. 4E). The initial substrate in silicon 30 is then removed, bychemical etching for example. Sensing elements are then obtainedcontaining a membrane 38 attached to a peripheral part 39. Cross cuttingof the final substrate will separate the sensing elements.

FIGS. 5A to 5C are cross sections illustrating a third method for theembodiment of the sensing elements. For the same reason as previously,only the fabrication of one sensing element is shown.

This third method starts in the same way as the second method. Bumps 41of blunt cone shape are made on the upper surface of a substrate 40, insilicon for example. A layer 42 of polycrystalline silicon carbide isthen deposited using a CVD technique for example and is levelled. Asshown in FIG. 5A this levelling only concerns layer 42. It may be madeby mechanical-chemical polishing to ensure proper control over thethickness of the polycrystalline silicon carbide positioned above thebumps 41.

Then, on layer 42, an insulating interface layer 43 (in silica forexample) is deposited as shown in FIG. 5B. A layer of monocrystallinesilicon carbide is transferred to the interface layer 43 using forexample the transfer method disclosed in document FR-A-2 681 472 citedabove. The epitaxy step of the previously described methods is notnecessary. Pieozresistive gauges 44 are formed in this layer ofmonocrystalline silicone carbide which may be etched so that only thegauges subsist.

As shown in FIG. 5C, electric contacts 45 are made for thepiezoresistive gauges 44. The initial substrate 40 in silicon is thenremoved, by chemical etching for example. This leads to obtainingsensing elements comprising a circular membrane 48 attached to aperipheral part 49. Cross cutting of the final substrate makes itpossible to separate the sensing elements.

By applying the transfer method disclosed in document FR-A-2 681 472 tothese three methods of embodiment, it is possible to produce a membranecontaining monocrystalline SiC on a passive substrate of a differentnature. The SiC membrane has the following intrinsic advantages:chemical inertia and resistance to aggressive chemical environments,resistance to high temperature, good mechanical resistance, goodelectric resistance of the gauges. The passive substrate may be chosenin relation to the intended application. For example, a substrate inpolycrystalline SiC will have the same chemical and mechanicalproperties as the membrane and is a good choice for applications in ahostile medium.

What is claimed is:
 1. Pressure sensor able to operate at hightemperature and to measure the pressure of a hostile medium, comprising:a sensing element integrating a membrane in monocrystalline siliconcarbide and made by micro-machining a substrate in polycrystallinesilicon carbide, a first surface of the membrane being intended to be incontact with said medium, a second surface of the membrane comprisingdetection means to detect membrane deformation and connected to electriccontacts to connect electric connection means, the surfaces of thesensing element intended to be in contact with the said medium beingchemically inert relative to this medium; a carrier supporting thesensing element so that said first surface of the membrane may be placedin contact with said medium and said second surface of the membrane maybe shielded from contact with said medium, the carrier being inpolycrystalline silicon carbide; a seal strip, in material containingsilicon carbide, brazed between the carrier and the sensing element toshield the second surface of the membrane from any contact with saidmedium.
 2. Pressure sensor according to claim 1, in which the sensorbeing intended to measure absolute pressure, the carrier comprises asealed closing part so that a vacuum may be set up inside the carrier.3. Pressure sensor according to claim 1, in which the carrier istube-shaped, the sensing element closes one of the tube ends, the firstsurface of the membrane being directed towards the outside of the tube.4. Pressure sensor according to claim 3, in which the carrier comprisesa thread so that it can be screwed to a reservoir containing the medium.5. Pressure sensor according to claim 1, in which an insulatinginterface layer is provided between the membrane and the substrate partof the sensing element.
 6. Pressure sensor according to claim 5, inwhich the insulating interface layer is in a material chosen from amongsilicon oxide, silicon nitride and carbon-containing silicon. 7.Pressure sensor according to claim 1, in which said electric contactsare in a silicide containing tungsten.
 8. Pressure sensor according toclaim 1, in which the connection between the electric contacts and theelectric connection means is obtained with a solder material whichwithstands high temperatures.
 9. Pressure sensor according to claim 8,in which said solder material is a silicide containing tungsten. 10.Pressure sensor according to claim 1, in which conductor means areprovided, forming a spring to ensure the connection between the electriccontacts and the electric connection means.
 11. Pressure sensoraccording to claim 1, in which said detection means comprise at leasttwo piezoresistive gauges.
 12. Pressure sensor according to claim 11, inwhich said piezoresistive gauges are in monocrystalline silicon carbide.